DISSIPATIVE TUNNELING CONTROL BY ELLIPTICALLY POLARIZED FIELDS

The tunneling dynamics of a dissipative two-level system that is stron gly driven by elliptically polarized electric fields is investigated. The dissipative dynamics is governed within the noninteracting-blip-ap proximation for the stochastic forces by a generalized master equation (GME). With the focus being on viscous friction, we compare exact num erical solutions of the GME with analytical approximations to both the transient and the asymptotic, long-time periodic dynamics. Novel phen omena are identified: These are a selective control on localization (o r, as well, on delocalization) of the tunneling dynamics, or the inver sion of an initially induced localization by a static bias via multiph oton-assisted tunneling. These effects can be selectively tuned as a f unction of the eccentricity parameter p = E-y/E-x of corresponding fie ld amplitudes. In particular, the case of a circularly polarized drivi ng field with p = +/- 1 yields a dramatic enhancement of the relaxatio n rate at resonances, when an integer multiple of the angular driving frequency matches the asymmetry energy induced by a static bias. (C) 1 998 American Institute of Physics.